Wii U is a good system to collect for. Im about 60 games in. The system is actually a really well done piece of hardware. The controller is kind of like a switch where you can play somewhat portable around your house, depending on the game. So, if you don't want to sit in front of TV all the time, its nice. It can play Wii games natively and Gamcube games (no discs) kind of natively via hombrew. It's not bad for emulating the other Nintendo systems as well. So, it's a good all around machine if you don't want to have everything set up all at once. Ive heard some people complain about disc read errors but I haven't experienced this yet. There's not much in the way of game variant hunting though which is sad. There's some officially refurbished games, some players choice games, and a few other random titles.
Honestly, game gear is next on my list after I finish my Gameboy set. I was really wanting to finish the other gameboy sets but there is just so much junk with gameboy color, gameboy advance, and nds that I will not bother with those right now. I had a game gear maybe 15 years ago. I dont particularly remember much standing out in the library but that just means there's some titles to visit/revisit.